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Influence of capillary conductivity and depth of wetting on moisture retention in soil

1952; American Geophysical Union; Volume: 33; Issue: 4 Linguagem: Inglês

10.1029/tr033i004p00531

2379-6723

L. A. Richards, Darren Moore,

Groundwater flow and contamination studies

The storage of moisture in soil in the field is discussed and explained in terms of the dynamic moisture‐transmitting properties of the soil. Published data on capillary conductivity (unsaturated permeability) are summarized and additional new data for six soils are presented, along with a new pressure‐type apparatus for measuring capillary conductivity. After a deep permeable soil is wetted in the field, the moisture content soon reduces to a value referred to as field capacity which thereafter changes relatively slowly with time. This field‐capacity condition apparently corresponds to the moisture content and moisture tension at which the capillary conductivity of the soil becomes small. Changes thereafter depend on the hydraulic gradient and the low residual values for the conductivity. These, of course, depend on the moisture distribution in the whole profile. A laboratory procedure sometimes used for estimating field capacity consists in measuring the moisture content of a mass of soil that has been wetted and allowed to stand a specified time in contact with dry soil. The dependence of this method on the depth of wetting is illustrated by laboratory tests on three soils and the explanation for this dependence appears to lie in the fact that the capillary conductivity of soils remains appreciable over a considerable range of moisture content below field capacity.